\documentclass{ctexbeamer}
\usetheme{sjtubeamer}
\begin{document}
\setbeamertemplate{sectioning pages}[maxplus]
\part{maxplus} \setbeamertemplate{sectioning pages}[max]
\part{max} \setbeamertemplate{sectioning pages}[min]
\setbeamertemplate{background}{}
\part{min}
\end{document}